The present invention relates to the technical field of printing media, particularly printing media free from release papers.
Narrow printing media having an adhesive layer have been widely used to print names or prices.
Reference 110 in FIG. 9(a) represents an example of a printing medium of the prior art, comprising a base film 111 for receiving ink, an adhesive layer 113 formed on the bottom of said base film and a release film 115 applied on the surface of adhesive layer 113.
This printing medium 110 is mounted on a printer and ink 117 is transferred onto the top surface of base film 111 in a desired pattern via a heat transfer film or the like (FIG. 9(b)).
Printing medium 110 having ink 117 transferred onto the top surface of base film 111 is delivered outside the printer, and then printing medium 110 is cut into an appropriate length and release film 115 is separated to expose the surface of adhesive layer 113 (FIG. 9(c)).
Then, the surface of adhesive layer 113 is pressed against the surface of a substrate 119 so that printing medium 110 representing a name or the like by ink 117 is adhered to substrate 119 (FIG. 9(d)).
However, release film 115 is discarded as waste and may generate hazardous materials upon incineration. The same problem may occur if printing medium 110 on substrate 119 becomes unnecessary and should be removed for disposal. Especially when base film 111 consists of a polyester resin and adhesive layer 113 consists of an acrylic resin, a typical disposal method is incineration for volume reduction.
A possible solution is to prepare a printing medium by applying an adhesive tape under recent study having a biodegradable base film or release film, which is spontaneously degraded by microorganisms after disposal.
However, any commercial printing media have not been obtained because of the low adhesion between the biodegradable film and the adhesive layer.
Adhesion is slightly improved by corona treatment on the surface of the base film, but the effect is relatively small for plant investment.
An object of the present invention is to overcome the above disadvantages of the prior art and to provide a biodegradable printing medium.
We found that when an adhesive layer is formed on the surface of a biodegradable film such as a polylactic acid film or a Bionolle film after it is rubbed with a rubbing means such as a cotton cloth or a buff (nylon brush), the adhesive strength (peel strength) between the film and the adhesive layer is improved. Such rubbing treatment is common for controlling the orientation of liquid crystal, but has not been applied to solids or semisolids such as an adhesive layer.
Contrary to the conventional rubbing treatment in the same direction, the present invention needs no directivity.
On the basis of the above finding, the present invention provides a printing medium comprising a base film and an adhesive layer formed on one side of the base film while the other side of the base film forms a printable face, wherein a surface of the base film is subjected to rubbing treatment with a rubbing means and then the adhesive layer is formed on a rubbed surface and the printing medium is wound into a roll wherein the adhesive layer and the printable face of the base film are in close contact with each other.
The present invention provides the printing medium wherein the adhesive layer is formed by applying and then drying an adhesive layer starting solution containing an adhesive in an organic solvent on the rubbed surface of the base film.
The present invention provides a printing medium comprising a base film, a primer layer formed on one side of the base film and an adhesive layer formed on a surface of the primer layer while the other side of the base film forms a printable face, wherein a surface of the base film is subjected to rubbing treatment with a rubbing means and then the primer layer is formed on a rubbed surface and the printing medium is wound into a roll wherein the adhesive layer and the printable face of the base film are in close contact with each other.
The present invention provides the printing medium wherein the primer layer contains a biodegradable colorant.
The present invention provides the printing medium wherein the primer layer is formed by applying and then drying a primer layer starting solution containing an adhesive in an organic solvent on the rubbed surface of the base film.
The present invention provides the printing medium wherein the adhesive layer is formed by applying and then drying an aqueous adhesive layer starting solution on the primer layer.
The present invention provides the printing medium wherein the base film is biodegradable.
The present invention provides the printing medium wherein the adhesive layer does not inhibit the biodegradability of the base film and contains an opaque filler.
The present invention provides the printing medium wherein the base film has a polylactic acid film and the surface of the polylactic acid film is subjected to the rubbing treatment.
The present invention provides the printing medium wherein the polylactic acid film is a biaxially oriented polylactic acid film.
The present invention provides the printing medium wherein the base film has a Bionolle film and the surface of the Bionolle film is subjected to the rubbing treatment.
The present invention provides the printing medium wherein adhesive components contained in the adhesive layer are based on an adhesive not inhibiting the biodegradability of the base film.
The present invention provides the printing medium wherein the adhesive is natural rubber.
The present invention provides the printing medium wherein the adhesive is a polyisoprene rubber.
The present invention provides the printing medium wherein the adhesive layer contains an antiaging agent.
The present invention provides the printing medium wherein the printable face is subjected to rubbing treatment with a rubbing means.
The present invention provides the printing medium wherein a biodegradable receiving layer is formed on the surface of the printable face.
Thus, the present invention provides a printing medium comprising a base film consisting of a biodegradable film such as a polylactic acid film or a Bionolle film and an adhesive layer disposed on one side of the base film while the other side forms a printable face.
The surface of the base film is rubbed with a rubbing means desired times and then a primer layer starting solution or an adhesive layer starting solution is applied and dried on the rubbed surface. Therefore, the adhesion between the primer layer or adhesive layer and the base film is increased.
If a printing medium of the prior art is wound into a roll without using a release film, only the base film is separated while the adhesive layer remains on the roll side because of the low adhesion between the biodegradable film and the adhesive layer when the printing medium is delivered for use.
In printing media of the present invention, the adhesive layer and the base film are not separated because the adhesion between the base film and the adhesive layer is increased by subjecting the surface of the base film to rubbing treatment.
The biodegradable base film is typically clear. When an opaque printing medium is to be manufactured, it is preferable to add a filler or colorant not inhibiting the biodegradability of the base film, adhesive layer and primer layer to the adhesive layer or primer layer.
Experiments proved that when the adhesive layer starting solution contains water as a solvent, the adhesion between the adhesive layer and the base film is not increased even if the surface of the base film is rubbed and the adhesive layer starting solution is applied and dried on the rubbed surface. In this case, it is preferable to apply a primer layer starting solution containing an adhesive in an organic solvent on the rubbed surface of the base film to form a primer layer followed by forming adhesive layer on the surface of the primer layer.
The primer layer may have a smaller thickness than that of the adhesive layer to reduce the amount of organic solvents used for manufacturing a printing medium.
The effect of rubbing treatment on the improvement of the adhesion between the base film and the adhesive layer is attained with not only biodegradable films but also resin films such as polyester films or polyimide films. Rubbing treatment is especially effective when a rubber-based adhesive layer is formed on the surface of such a resin film.